Flickerless three-phase lighting device for electric discharge lamps

ABSTRACT

The invention concerns a flickerless discharge lamp lighting device which utilizes a three-phase to two-phase converter capable of converting three-phase current into a two-phase current with a phase difference of 90*.

Ullltfid States Patent 1 91 Nakai et al.

[451 Apr. 3, 1973 [54] FLICKERLESS THREE-PHASE LIGHTING DEVICE FOR ELECTRIC DISCHARGE LAMPS [75] Inventors: Kenichi Nakai, Neyagawa; Takehiko Yamasliita, lchikawa, both of Japan [73] Assignee: Matsushita Electric Works, Ltd.,

Osaka, Japan 221 Filed: Dec. 23, 1971 211 App]. No.: 211,510

[30] Foreign Application Priority Data Dec. 28, 1970 Japan ..45/l30583 [52] US. Cl .L ..3l5/144, 315/138 [51] Int. Cl. ..H05b 41/16 [58] Field of Search ..3l5/l44, 141, 137,139, 138

Primary Examiner-John Kominski AttorneyWolfe, Hubbard, Leydig, Voit & Osann, Ltd.

[57] ABSTRACT The invention concerns a flickerless discharge lamp lighting device which utilizes a three-phase to twophase'converter capable of converting three-phase current into a two-phase current with a phase difference of 90.

4 Claims, 19 Drawing Figures PATH-HEB APR3 m3 SHEET 1 OF 7 F/g. PRIOR ART 1C Hg 2 PRIOR ART 26 ZOTZZEDJ m0 tmzmE/z PATENTEUAPR3 1975 3,725,730

SHEET 3 [1F 7 PATENIEDAPR3 1975 3,725,730

sum 5 UF 7 Fig. /2

INTENSITY OF ILLUMINATION FLICKERLESS THREE-PHASE LIGHTING DEVICE FOR ELECTRIC DISCHARGE LAMPS This invention relates in general to flickerless lighting device for electric discharge lamps operated from a three-phase AC source.

The flickerless lighting device for discharge lamps is generally of the type that two discharge lamps are lighted simultaneously at lamp currents provided with a certain phase difference, thereby reducing the light ripple component and thus preventing the optical nerve from being fatigued.

The effect of ideally removing flicker can be obtained when the phase difference between the lamp currents to the two discharge lamps is 90, where the light ripple component is minimized.

However, this type of discharge lamp apparatus using a phase-advancing element as shown in FIG. 1 is practically unable to make the lamp current phase difference to be 90 though it is theoretically possible.

The conventional discharge lamp lighting devices in general are of single-phase. To energize such lighting device from a three-phase AC source, consideration is necessary so that an equal number of loads will be connected to the individual phases, R, S and T, in order to balance the currents on the respective phases.

Practically, however, in the following instances it is impossible to establish current balance on three phases:

i. The number of loads of discharge lamp cannot be evenly divided by three.

ii. The number of loads is two.

In the practical installation of the lamp apparatus in three-phase system, the lamp loads are often incorrectly connected with respect to phase by those whose electrical knowledge is not always competent. This leaves current unbalance on phases and often requires cumbersome reinstallation.

In view of the foregoing, the present invention has for its principal aim the provision of a flickerless discharge lamp lighting device in which an ideal phase difference of 90 is maintained for the currents supplied to the individual discharge lamps, thus realizing a complete flickerless effect and, at the same time, the current balance on three phases can be easily obtained. Briefly, to this end, the present invention utilized a three-phase to two-phase converter capable of converting a three-phase current into a two-phase current with a phase different of 90, and two discharge lamps being equal in the load rating are energized from a threephase AC source through said three-phase to twophase converter. With the lighting device of this invention, therefore, all the foregoing problems in the prior art can be solved.

A principal object of this invention is therefore, to provide a discharge lamp lighting device with which a complete flickerless effect can be expected.

Another object of the invention is to provide a flickerless discharge lamp lighting device which is easily installable and capable of being free of any current unbalance on the respective three phases.

Another object of the invention is to provide a flickerless discharge lamp lighting device capable of establishing 90 phase difference between currents of two-phase.

Still another object of the invention is to provide a flickerless discharge lamp lighting device for which installation requires only a relatively simple, and therefore smaller, power supply system.

Other objects, features and advantages of the invention will become more apparent upon reading the following descriptions detailed with reference to the accompanying drawings, in which:

FIG. 1 is a circuit diagram showing a conventional flickerless discharge lamp lighting device,

FIGS. 2 and 3 are diagrams showing the operation of the flickerless discharge lamp lighting device as in FIG.

FIG. 4 is a circuit diagram showing a three-phase to two-phase converter used in the present invention,

FIGS. 5 through 10 are diagrams showing the operation of the discharge lamp lighting device according to the present invention,

FIG. 11 is an embodiment of the present invention,

FIG. 12 is a diagram showing the operation of the lighting device as in FIG. 1 1,

FIG. 13 is a circuit diagram showing another embodiment of the invention,

FIG. 14 is a diagram showing the operation of the embodiment as in FIG. 13,

FIG. 15 is a circuit diagram showing a further embodiment of the invention, v

FIGS. 16 through 18 are diagrams showing the operation of the embodiment as in FIG. 15, and

FIG. 19 is a circuit diagram showing yet another embodiment of the invention.

Referring now to FIG. 1, there is shown a conventional flickerless discharge lamp lighting device, wherein a-series circuit 'of discharge lamp 3 and a phase-lagging current-limiting means comprising a choke coil 2, and a series circuit of a discharge lamp 6 and a phase-leading current-limiting means comprising a choke coil 4 and a capacitor 5 are connected across a single-phase AC source 1, which two current-limiting means are constituted integral into one stabilizer 7. The discharge lamp 3 is supplied with a phase-lagging lamp current I,, as shown in FIG. 2 via said phase-lagging current-limiting means, and the discharge lamp 6 is supplied with a phase-leading lamp current I via said phase-leading current-limiting means. With this arrangement, it is intended that the lamp light beams F and F produced from the lamp currents I L and I standing mutually at different phases are combined as shown in FIG. 3 and, thus, a flickerless light beam F whose light value is not much changeable and ripple component is much reduced.

In this type of flickerless discharge lamp lighting device, the flickerless effect is to reduce the light ripple component, and its effect is made to be the largest when the phase difference between the lamp currents I and I L is chosen to be so that the maximum value of the light beam F and the minimum value of the light beam F will coincide with each other with respect to phase. Practically, the currents I and I supplied to the discharge lamps 3 and 6 are deviated in phase about 60 respectively from the power source voltage E as seen in FIG. 2. Namely, there is a phase difference of about between the two currents I and I which difference has been making it impossible to realize an ideal flickerless effect in the art. This problem is attributed to certain factors in making the current-limiting means cheaper and smaller, as well as other factors in selecting the constants of such means.

The present invention has been suggested, in view of the above problem, to provide a discharge lamp lighting device which performs an ideal flickerless effect with a remarkably simplified circuit structure.

Referring to FIG. 4, there is shown an embodiment of phase converter used in the present invention, wherein 11 is a three-phase AC source, and 12 and 15 are single-phase transformers having n turns of primary windings 13 and 16 and n, turns of secondary windings l4 and 17, respectively. 18 and 19 are respectively equal loads connected to the secondary windings 14 and 17 of said single-phase transformers, and 20 is a choke coil whose number of turns is fin The primary windings 13 and 16 said transformers and the choke coil 20 form a closed circuit. The connection point a between the primary windings 13 and 16, and the points b and c where the choke coil 20 is divided at the turnratio of(l/ Vim 1/ V 2/ V5; '1/ im (1] are connected to the three-phase AC source output terminals, respectively, to form a phase converter.

Using this phase converter, balanced two-phase voltages are obtained in the following manner.

FIG. 5 is a circuit diagram showing balanced threephase loads wherein choke coils 21, 22 and 23 each having an equal n'-number of turns are connected in delta form. Across these coils, voltages V V and V having a phase deviation of l20 from each other are produced as shown in FIG. 6. The number of turns of the choke coil 23 is increased to fin from n, and divided into three parts at the ratio (l/ 2) [1 ll 3- 2/ 3: (l/ 63H l/ 3. At the pointsbandc dividing the coil in such ratio, the coil is connected to two lines of the three-phase AC source. The choke coil 23 is made to have its outermost ends at the points d and e, to which the choke coils 21 and 22 whose numbers of turns are equally n are connected. The voltage relationship in this delta connection is shown by a vector diagram in FIG. 8, wherein the voltage across the choke coils 21 and 22 is represented by the difference voltage (Vac Vce) whose value is 3/ 2 V0 when the absolure value of each of the voltages Vab and Vac is represented by V0, and the angle formed between the voltages Vab and Vac will be In other words, the voltages V and V across the choke coils l1 and 12, respectively, are equal in the value and different in the phase by 90. Thus balanced two-phase voltages are obtained on the arms ac and ad.

FIG. 9 shows a circuit similar to the one in FIG. 4, in which current relationship is made in such that the currents flowing into the points a, b and 0, respectively, from the three-phase AC source 1 will be I I, and I and the currents flowing from the point e to a, b to a, and b to c will be Ia, Ib and 10, respectively. Further, the currents flowing through the loads 18 and 19 are made to be [W and In. Under this condition, the following equations are established between these currents:

n lw n Ib 0 V2 V3 V3 #2 V3 Eliminating Ia, lb and Ic, the currents 1,, I and I are given in terms of la and Iw as follows:

Since the loads 18 and 19 are mutually equal, the load currents Ia and Iw are equal in the value and different in the phase by 1r/2. Let the scalar value of the current be I. Then,

1I11=1 1u+1 I m M Namely, the currents I 1 and 1 are equal to each other in the absolute value. Each of the angles formed between individual twos of 1,, I, and I is 120?, which is derived from the formula tan B V1 thus B= and 75 45 120. The currents I 1 and 1;, are equalized and perfectly balanced at a phase difference of 120. This relationship is shown by a vector diagram in FIG. 10.

In the above embodiment, while the numbers of turns n and 2n are employed for the single-phase transformers and choke coils, for the sake of simplicity of explanation, it should be noted that a conversion into balanced voltages of two phases can be performed by simply controlling the dividing ratio of the choke coil 23, in accordance with the present invention.

Utilizing the foregoing phase converter, the present invention successfully provides an ideal three-phase flickerless discharge lamp lighting device.

In the prior art, the flickerless discharge lamp lighting device uses a single-phase AC source, and comprises in combination a discharge lamp device having a stabilizer of an inductive impedance such as choke coil or the like, and another discharge lamp device having a stabilizer of a capacitive impedance including a capacitor, so that the light ripple component is minimized when the light beams of the two discharge lamps are combined. To ideally attain this aim, it is necessary to maintain the phase difference between the currents of the two discharge lamps to be Practically, however, there are difficulties in determining the constants of the discharge lamps and stabilizers, and in. obtaining an ideal flickerless performance.

According to the present invention, an ideal flickerless performance can easily be obtained. FIG. 11 shows by circuit diagram an embodiment of such flickerless discharge lamp lighting device of the present invention. In FIG. 11, the device shown in FIG. 4 is arranged such that the current-limiting means, i.e., choke coils 21 and 22 having the same characteristics are connected to one ends of the secondary windings l4 and 17 of singlephase transformers l2 and 15, respectively, and discharge lamps 23 and 24 are connected to a threephase AC source through said coils 21 and 22. As will be evident from references to FIG. 4, load currents equal in the value and different in the phase by 90 are obtained at the respective loads when the loads of the single-phase transformers 12 and are exactly the same. Therefore, lamp currents equal in the value and different in the phase by 90 are caused to flow in the discharge lamps 23 and 24, respectively, and the light beams L and L from the discharge lamps 23 and 24 are accurately phase-deviated by 90 from each other as shown in FIG. 12. Thus the light beams L and L are mutually complementary with respect to their variation components, and the combined light beam L comes out with a minimized ripple component, giving no appreciable flicker, so that the desired flickerless effect can be established.

FIG. 13 illustrates another embodiment of this invention. This embodiment uses a first single-phase transformer 31 having n turns of primary winding 28, v3 1 NE 1n, turns of auxiliary winding 29, and n, turns of secondary winding 30 respectively wound on a common iron core, and a second single-phase transformer 35 having n turnsof primary winding 32, V3 l)/ 2 n turns of auxiliary winding 33, and n turns of secondary winding 34 respectively wound on the other common iron core. The primary winding 28 and auxiliary winding 29 of the first single-phase transformer 31, and the auxiliary winding 33 of the second single-phase transformer 35 are connected in series to each other, and one end of the primary winding 32 of the second single'phase transformer 35 is connected to the connection point a of the first primary winding 28- and auxiliary winding 29. The other end c of the auxiliary winding 33 of the second single-phase transformer 35, the other end d of the primary winding 28 of the first single-phase transformer 31, and the other end e of the primary winding 32 of the second single-phase transformer 35 are utilized as power source terminals to be connected to the three-phase AC source 36. The first single-phase discharge lamp device 41 comprising a current-limiting means 37 and a discharge lamp 38, and the second single-phase discharge lamp device 42 comprising a current-limiting means 39 and a discharge lamp 40 are connected to the secondary windings 30 and 34 of the single-phase transformers 31 and 35,

respectively.

In this apparatus, it is assumed that three-phase voltages Vcd, Vde and Vec having mutually the same values V0 and a phase difference of l are applied to the input terminals c, d and e from a three-phase AC source 36. FIG. 14 shows the relationship between the voltage Vad across the primary winding 28, the voltage Vba across the auxiliary winding 29, the voltage Vea across the primary winding 32, and the voltage Vac across the auxiliary winding 33. The voltages Vad and Vea are equal to each other since the primary windings 28 and 32, and the auxiliary windings 29 and 33 of the singlephase transformers 31 and 35 are equal in the number of turns. The voltage Vbd between the points I; and d is represented by 3- 1)/ V2 V where V is the value of Vad and Vea, because Vad and Vba are the voltages produced across the windings on the same core and equal in the phase. The voltage Vbc is represented by 3 l)/ V2 V If the angle formed between the voltages Vad and Vea is the value V0 of the voltage Vcd should be 2 V When this relationship is applied to the boltages Vad, Vea and Vde, then V V V 2 V V0. This evidences that 90 is the justly reasonable angle formed between the voltages Vad and Vea. Hence it is apparent that the voltages across the primary windings 28 and 32 and across the auxiliary windings 29 and 33 of the singlephase transformers 31 and 35 are equal in the value and different in the phase by 90. Accordingly the secondary voltages Eu and Ew induced across the secondary windings 30 and 34 of the single-phase transformers 31 and 35are equal in the value and different in the phase by 90. The first and second single-phase discharge lamp devices 41 and 42 having mutually the same loads are driven by the voltages Eu and Ew.

Therefore, currents equal in the value and different in the phase by 90 are caused to flow in the discharge lamps 38 and 40, respectively, whereby an ideal flickerless effect is established.

FIG. 15 shows another embodiment of the invention, wherein a power source choke coil 49 is connected via terminals d and 2 between S-phase and T-phase of a three-phase AC source 48 having R, S and T phases. This choke coil is divided at the point a at the ratio of [l (\/fi)]z\/fi. The part corresponding to \/3/2 is connected in parallel to a discharge lamp device 52 comprising a current-limiting means 50 and a discharge lamp 51. A discharge lamp device 53 having the same characteristic as that of the discharge lamp device 52 is'connected between the center point b of the choke coil 49 and the terminal 0 to which the R- phase is connected.

In this arrangement, the currents flowing in the discharge lamps 52 and 53 respectively are equal in the value and different in the phase by 90, whereby an ideal flickerless characteristic can be obtained. The apparatus will be more specifically described below.

In the circuit of FIG. 16, the current flowing and the voltage appearing in the circuit in FIG. 15 are deter- 52 and 53 will be V and V The following relationships are established among these currents:

From the above equations,

On the other hand, as shown in FIG. 17, V is the voltage produced between the center point b of the voltage Vde in the voltages Vde, Vec and Ved having phase differences of 120 and the point c, in the direction from b to 0. At this time, the value of voltage V, is represented by V sin 60, i.e., 3/ 2)V0, where V is a line voltage. In other words, the voltage V is dire c tionally coincided with the voltage Vde and is \/3/2 the value ofvoltage Vde,with aphase difference of 90. FIG. 18 is a vector diagram indicating the relationship among the currents I I and I obtained according to the foregoing equations on currents I I and I to which the principle that the current I and I to flow when the voltage V and V are applied to the same loads are equal in the value and dirrerent in the phase by 90 is applied. In FIG. 18, the angle B formed between the currents I and I should be 30 according to the following equation:

1 5 1l inn [3:

v/: l l

Then the current values are determined as Thus the currents I I and I are different in the phase by 120 and equal in the value, and the three-phase currents supplied to the discharge lamp apparatus are balanced. It is therefore apparent that illumination of the discharge lamps 52 and 53 is free of flickering.

FIG. 19 illustrates snother embodiment of the invention utilizing so-called Scott connection, wherein 60 is a three-phase AC source, 61 is a single-phase transformer, 62 is the primary winding thereof, 63 is the secondary winding thereof, 64 and 65 are a currentlimiting means and a discharge lamp respectively connected to the secondary winding 63, 66 is another single-phase transformer, 67 is the primary winding thereof, 68 is the secondary winding thereof, and 69 and 70 are a current-limiting means and a discharge lamp respectively connected to the secondary winding According to the present invention, as has been described above, a three-phase to balanced two-phase converter is employed, the output of said phase converter is provided with a phase difference of 90 and current-limiting means and discharge lamp units of the same characteristics are connected to the output side of the convertor, whereby a constructionally simple, three-phase driven and flickerless discharge lamp lighting device can be obtained.

While the principles of the invention have been described above in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

What is claimed is: 1. A fiickerless type three-phase lighting device for discharge lamps comprising a three-phase AC source; a

three-phase to balanced two-phase converter connected to said AC source and capable of providing at its output terminals the voltages having phase differences mutually of and current-limiting means and discharge lamps operable respectively in the identical characteristics, said means and lamps being connected to the output terminals of said three-phase to balanced two-phase converter.

2. A discharge lamp lighting device as defined in claim 1, in which said three-phase to balanced twophase converter comprises two single-phase transformers each having a secondary winding of n turns and a primary windin of n turns, and a choke coil having a winding of 2 n turns, the primary windings of said transformers and said choke coil are connected in delta form, and the three-phase AC source is connected to the connection point of the primary windings of the both single-phase transformers and also to the points at which said choke coil is divided into three parts at the turn ratio of a primary winding of drums. an auxiliary winding of -l)/2]n turns and a secondary winding all wound commonly on an iron core, and a second single-phase transformer having a primary winding of n turns, an auxiliary winding of 1)/2]n turns and a secondary winding all wound commonly on an iron core; said primary winding and auxiliary winding of said first single'phase transformer, and said auxiliary winding of said second single-phase transformer are sequentially connected in series to each other, one end of the primary winding of said second single-phase transformer is connected to the connection point of the primary winding and the auxiliary winding of said first single-phase transformer, and the other end of the primary winding of said first single-phase transformer, the other end of the auxiliary winding of said second single-phase transformer, and the other end of the primary winding of said second single-phase transformer are used as the power source terminals for the three-phase AC source.

4. A discharge lamp lighting device as defined in claim I, in which said choke coil is divided at the ratio of V 3/2 [l 3 2 first current-limiting means and discharge lamp unit are connected inparallcl to the choke coil part corresponding to 372, the second current-limiting means and discharge lamp unit whose characteristics are the same as those of the first current-limitingmeans and discharge lamp unit are connected to the center point of said choke coil, and a three-phase power is supplied across said choke coil and to the other terminal of said second unit. 

1. A flickerless type three-phase lighting device for discharge lamps comprising a three-phase AC source; a three-phase to balanced two-phase converter connected to said AC source and capable of providing at its output terminals the voltages having phase differences mutually of 90*; and current-limiting means and discharge lamps operable respectively in the identical characteristics, said means and lamps being connected to the output terminals of said three-phase to balanced two-phase converter.
 2. A discharge lamp lighting device as defined in claim 1, in which said three-phase to balanced two-phase converter comprises two single-phase transformers each having a secondary winding of n2 turns and a primary winding of n1 turns, and a choke coil having a winding of Square Root 2 n2 turns, the primary windings of said transformers and said choke coil are connected in delta form, and the three-phase AC source is connected to the connection point of the primary windings of the both single-phase transformers and also to the points at which said choke coil is divided into three parts at the turn ratio of ( 1/ Square Root 2) (1 - (1/ Square Root 3)) : Square Root 2/ Square Root 3 : (1/ Square Root 2) (1 - (1/ Square Root 3) ).
 3. A discharge lamp lighting device as defined in claim 1, in which said three-phase to two-phase converter comprises a first single-phase transformer having a primary winding of n turns, an auxiliary winding of ( Square Root 3 - 1)/2 )n turns and a secondary winding all wound commonly on an iron core, and a second single-phase transformer having a primary winding of n turns, an auxiliary winding of ( Square Root 3 - 1)/2)n turns and a secondary winding all wound commonly on an iron core; said primary winding and auxiliary winding of said first single-phase transformer, and said auxiliary winding of said second single-phase transformer are sequentially connected in series to each other, one end of the primary winding of said second single-phase transformer is connected to the connection point of the primary winding and the auxiliary winding of said first single-phase transformer, and the other end of the primary winding of said first single-phase transformer, the other end of the auxiliary winding of said second single-phase transformer, and the other end of the primary winding of said second single-phase transformer are used as the power source terminals for the three-phase AC source.
 4. A discharge lamp lighting device as defined in claim 1, in which said choke coil is divided at the ratio of Square Root 3/2 : (1 - ( Square Root 3/2)), first current-limiting means and discharge lamp unit are connected in parallel to the choke coil part corresponding to Square Root 3/2, the second current-limiting means and discharge lamp unit whose characteristics are the same as those of the first current-limiting means and discharge lamp unit are conNected to the center point of said choke coil, and a three-phase power is supplied across said choke coil and to the other terminal of said second unit. 